The invention pertains to a method for the production of a highly stressable component from an α+γ-titanium aluminide alloy for reciprocating-piston engines and gas turbines, especially for aircraft engines.
Alloys based on TiAl belong to the group of the intermetallic materials, which were developed for applications at the working temperatures where superalloys are currently being used. Because of their low density of about 4 g/cm3, this material offers considerable potential for weight reduction and for the reduction of the stresses of moving parts such as the blades and disks of gas turbines or components of piston engines at temperatures of up to approximately 700° C. The precision casting of turbine blades for aircraft engines, for example, belongs to the prior art. For applications with even greater loads such as those on the high-speed turbines for the new geared turbofan aircraft engines, the properties of the cast structure are no longer sufficient. By means of thermomechanical treatment involving plastic forming with a defined degree of deformation followed by a heat treatment, the static and dynamic properties of TiAl alloys can be increased to the required values. Nevertheless, TiAl alloys, because of their high deformation resistance, cannot be forged in the conventional way. Therefore, the forming processes must be carried out at high temperatures in the area of the α+γ- or α-phase region under a shield atmosphere at low deformation rates. To achieve the desired final geometry of the forging, it is usually necessary to perform several forging steps in succession.
One example of a method of this type for the production of highly stressable components from α+γ-TiAl alloys is known from DE 101 50 674 B4. In this method, components intended in particular for aircraft engines or stationary gas turbines are produced by forming encapsulated TiAl blanks with a globular microstructure by primary isothermal deformation in the α+γ-phase region at temperatures in the range of 1,000-1,340° C. or in the α-phase region at temperatures in the range of range of 1,340-1,360° C. by forging or extrusion, after which the preforged parts are forged into their final shape in at least one secondary isothermal deformation process in the α+γ-phase or α-phase region at temperatures in the range of 1,000-1,340° C. under simultaneous dynamic recrystallization to obtain the component with the specified contour, after which the component is solution-annealed in the α-phase region to set the microstructure and then quickly cooled. A two-stage process is therefore carried out, comprising a primary deformation in the α+γ- or α-phase region, followed by a secondary deformation under simultaneous recrystallization. A two-stage process of this type, however, is extremely costly.